Usefulness of three-dimensional reconstruction for interpretation and quantitative analysis of intracoronary ultrasound during stent deployment

Freehand 3-D Ultrasound Imaging: A Systematic Review

Two-dimensional ultrasound (US) imaging has been successfully used in clinical applications as a low-cost, portable and non-invasive image modality for more than three decades. Recent advances in computer science and technology illustrate the promise of the 3-D US modality as a medical imaging technique that is comparable to other prevalent modalities and that overcomes certain drawbacks of 2-D US. This systematic review covers freehand 3-D US imaging between 1970 and 2017, highlighting the current trends in research fields, the research methods, the main limitations, the leading researchers, standard assessment criteria and clinical applications. Freehand 3-D US systems are more prevalent in the academic environment, whereas in clinical applications and industrial research, most studies have focused on 3-D US transducers and improvement of hardware performance. This topic is still an interesting active area for researchers, and there remain many unsolved problems to be addressed.

Modelling of image-catheter motion for 3-D IVUS

Three-dimensional intravascular ultrasound (IVUS) allows to visualize and obtain volumetric measurements of coronary lesions through an exploration of the cross sections and longitudinal views of arteries. However, the visualization and subsequent morpho-geometric measurements in IVUS longitudinal cuts are subject to distortion caused by periodic image/vessel motion around the IVUS catheter. Usually, to overcome the image motion artifact ECG-gating and image-gated approaches are proposed, leading to slowing the pullback acquisition or disregarding part of IVUS data. In this paper, we argue that the image motion is due to 3-D vessel geometry as well as cardiac dynamics, and propose a dynamic model based on the tracking of an elliptical vessel approximation to recover the rigid transformation and align IVUS images without loosing any IVUS data. We report an extensive validation with synthetic simulated data and in vivo IVUS sequences of 30 patients achieving an average reduction of the image artifact of 97% in synthetic data and 79% in real-data. Our study shows that IVUS alignment improves longitudinal analysis of the IVUS data and is a necessary step towards accurate reconstruction and volumetric measurements of 3-D IVUS.

Coronary intravascular ultrasound: implications for understanding the development and potential regression of atherosclerosis

The incremental value of intravascular ultrasound (IVUS), compared with angiographic analysis of coronary atherosclerosis, originates principally from 2 key features-its tomographic perspective and the ability to image coronary atheroma directly. Whereas angiography depicts the cross-sectional coronary anatomy as a planar silhouette of the lumen, ultrasound directly images the atheroma within the vessel wall, allowing measurement of atheroma size, distribution, and to some extent, composition. Although angiography remains the principal method to assess the extent of coronary atherosclerosis and to guide percutaneous coronary interventions, IVUS is rapidly altering conventional paradigms in the diagnosis and therapy of coronary artery disease. Thus, IVUS has become a vital adjunctive imaging modality for the aggressive coronary interventional cardiologist. As such, ultrasound has earned a role as a viable complementary technique relative to angiography, rather than an alternative to conventional angiographic methods. This article reviews the rationale, technical advantages and limitations, and interpretation of intravascular ultrasonography from the perspective of the general and invasive cardiologist. We emphasize the impact that IVUS studies have had on our understanding of the atherosclerotic coronary artery disease process, because these findings have important implications for all cardiologists. We then review several trials that are currently using intravascular ultrasonography for the study of coronary artery disease regression.

Quantitative measurements in IVUS images

IntraVascular UltraSound (IVUS) is a catheter-based technique which provides real-time high resolution tomographic images of both the lumen and arterial wall of a coronary segment, this in contrast to X-ray arteriography that provides a shadow image (luminogram) of the entire lumen. Nowadays the lumen and vessel parameters are measured manually, which is very time consuming and suffers from high inter- and intra-obser variability. With the continuing improvement in IVUS imaging, it is now feasible to develop and clinically apply automated methods of three-dimensional quantitative analysis of the coronary vessel morphology in an objective and reproducible way with automated contour detection techniques (QCU). Quantification, in 2D and 3D, as well as volume rendering for visualization of the IVUS images requires segmentation of the images (contour detection). The 3D contour detection system described in this article is based on the combination of contour detection in the transversal and sagital view. This article provides some of the basic principles of IVUS, the IVUS image quantification, the three-dimensional reconstruction and the contour detection and quantification in three-dimensional IVUS images.

Tissue characterization in intravascular ultrasound images

Intravascular ultrasound (IVUS) imaging permits direct visualization of vascular pathology. It has been used to evaluate lumen and plaque in coronary arteries and its clinical significance for guidance of coronary interventions is increasingly recognized. Conventional manual evaluation is tedious and time-consuming. This paper describes a highly automated approach to segmentation of coronary wall and plaque, and determination of plaque composition in individual IVUS images and pullback image sequences. The determined regions of plaque were classified in one of three classes: soft plaque, hard plaque, or hard plaque shadow. The method's performance was assessed in vitro and in vivo in comparison with observer-defined independent standards. In the analyzed images and image sequences, the mean border positioning error of the wall and plaque borders ranged from 0.13-0.17 mm. Plaque classification correctness was 90%.

Three-dimensional ultrasound imaging

The objective of this article is to provide scientists, engineers and clinicians with an up-to-date overview on the current state of development in the area of three-dimensional ultrasound (3-DUS) and to serve as a reference for individuals who wish to learn more about 3-DUS imaging. The sections will review the state of the art with respect to 3-DUS imaging, methods of data acquisition, analysis and display approaches. Clinical sections summarize patient research study results to date with discussion of applications by organ system. The basic algorithms and approaches to visualization of 3-D and 4-D ultrasound data are reviewed, including issues related to interactivity and user interfaces. The implications of recent developments for future ultrasound imaging/visualization systems are considered. Ultimately, an improved understanding of ultrasound data offered by 3-DUS may make it easier for primary care physicians to understand complex patient anatomy. Tertiary care physicians specializing in ultrasound can further enhance the quality of patient care by using high-speed networks to review volume ultrasound data at specialization centers. Access to volume data and expertise at specialization centers affords more sophisticated analysis and review, further augmenting patient diagnosis and treatment.

User-friendly and low-cost computer system for immediate review, analysis, and reconstruction of intracoronary ultrasound images

Rapid review, digital recording, on-line quantification, and three-dimensional reconstruction are all essential in the evaluation of intracoronary ultrasound images during coronary interventions. We describe a low-cost method that offers all these necessary features. The proposed method uses the QuickTime compatible video digitizers of standard multimedia Apple Macintosh or PowerPC desktop computers and the freeware software Object Image 1.60.

ECG-gated three-dimensional intravascular ultrasound: feasibility and reproducibility of the automated analysis of coronary lumen and atherosclerotic plaque dimensions in humans

BACKGROUND

Automated systems for the quantitative analysis of three-dimensional (3D) sets of intravascular ultrasound (IVUS) images have been developed to reduce the time required to perform volumetric analyses; however, 3D image reconstruction by these nongated systems is frequently hampered by cyclic artifacts.

METHODS AND RESULTS

We used an ECG-gated 3D IVUS image acquisition workstation and a dedicated pullback device in atherosclerotic coronary segments of 30 patients to evaluate (1) the feasibility of this approach of image acquisition, (2) the reproducibility of an automated contour detection algorithm in measuring lumen, external elastic membrane, and plaque+media cross-sectional areas (CSAs) and volumes and the cross-sectional and volumetric plaque+media burden, and (3) the agreement between the automated area measurements and the results of manual tracing. The gated image acquisition took 3.9+/-1.5 minutes. The length of the segments analyzed was 9.6 to 40.0 mm, with 2.3+/-1.5 side branches per segment. The minimum lumen CSA measured 6.4+/-1.7 mm2, and the maximum and average CSA plaque+media burden measured 60.5+/-10.2% and 46.5+/-9.9%, respectively. The automated contour-detection required 34.3+/-7.3 minutes per segment. The differences between these measurements and manual tracing did not exceed 1.6% (SD<6.8%). Intraobserver and interobserver differences in area measurements (n=3421; r=.97 to.99) were <1.6% (SD<7.2%); intraobserver and interobserver differences in volumetric measurements (n=30; r=.99) were <0.4% (SD<3.2%).

CONCLUSIONS

ECG-gated acquisition of 3D IVUS image sets is feasible and permits the application of automated contour detection to provide reproducible measurements of the lumen and atherosclerotic plaque CSA and volume in a relatively short analysis time.

Electrocardiogram-gated intravascular ultrasound image acquisition after coronary stent deployment facilitates on-line three-dimensional reconstruction and automated lumen quantification

OBJECTIVE

This study evaluates the feasibility, reliability and reproducibility of electrocardiogram (ECG)-gated intravascular ultrasound (IVUS) image acquisition during automated transducer withdrawal and automated three-dimensional (3D) boundary detection for assessing on-line the result of coronary stenting.

BACKGROUND

Systolic-diastolic image artifacts frequently limit the clinical applicability of such automated analysis systems.

METHODS

In 30 patients, after successful angiography-guided implantation of 34 stents in 30 target lesions, we carried out IVUS examinations on-line with the use of ECG-gated automated 3D analyses and conventional manual analyses of two-dimensional images from continuous pullbacks. These on-line measurements were compared with off-line 3D reanalyses. The adequacy of stent deployment was determined by using ultrasound criteria for stent apposition, symmetry and expansion.

RESULTS

Gated image acquisition was successfully performed in all patients to allow on-line 3D analysis within 8.7 +/- 0.6 min (mean +/- SD). Measurements by on-line and off-line 3D analyses correlated closely (r > or = 0.95), and the minimal stent lumen differed only minimally (8.6 +/- 2.8 mm2 vs. 8.5 +/- 2.8 mm2, p = NS). The conventional analysis significantly overestimated the minimal stent lumen (9.0 +/- 2.7 mm2, p < 0.005) in comparison with results of both 3D analyses. Fourteen stents (41%) failed to meet the criteria by both 3D analyses, all of these not reaching optimal expansion, but only 7 (21%) were detected by conventional analysis (p < 0.02). Intraobserver and interobserver comparison of stent lumen measurements by the automated approach revealed minimal differences (0.0 +/- 0.2 mm2 and 0.0 +/- 0.3 mm2) and excellent correlations (r = 0.99 and 0.98, respectively).

CONCLUSIONS

ECG-gated image acquisition after coronary stent deployment is feasible, permits on-line automated 3D reconstruction and analysis and provides reliable and reproducible measurements; these factors facilitate detection of the minimal lumen site.

Automated morphometry of coronary arteries with digital image analysis of intravascular ultrasound

We designed and tested digital image processing strategies to perform fully automated segmentation of luminal and medial-adventitial boundaries in intravascular ultrasound images of human coronary arteries. Automated segmentation is an essential tool for advanced techniques of clinical visualization and quantitative measurement. Vascular compliance measurements and three-dimensional reconstructions are demonstrated as examples of such applications. Digital image processing was performed in three phases: (1) preprocessing, including a polar transform, local contrast enhancement, and speckle noise filtering; (2) segmentation, involving radial scanning, region growing, or cost-function minimization techniques; and (3) postprocessing, involving dropout filtering and outline smoothing. Cross-sectional areas were compared with manual tracings from experienced operators and showed good agreement. The algorithm bias ranged from -0.34 to 1.18 mm2; interclass and intraclass correlation coefficients ranged from 0.83 to 0.94. The designed techniques currently allow fully automated segmentation without operator interaction of the luminal and, if present, medial-adventitial boundary.

Ultrasound-guided stent placement

IVUS imaging has dramatically increased understanding of the process of coronary stent placement. Preintervention or diagnostic IVUS has been shown to be of value before stent placement to assess lesion severity and length as well as the degree and location of calcification. Before stent placement, ultrasound dimensions may also be used to select the appropriate type and size of device. Although studies are in progress to define the role of prestent ultrasound imaging, much interest centers around the use of IVUS to detect significant superficial coronary calcium and direct rotational atherectomy before stent placement. Clinical trials have demonstrated the feasibility and safety of IVUS-guided coronary stent placement without postprocedure warfarin anticoagulation. Although it has been established subsequently that reduced anticoagulation may be administered to low-risk patients without IVUS guidance, three important points have been established by these trials. First, IVUS is superior to angiography for assessment of adequate stent expansion and apposition. As noted in several studies, angiography frequently overestimates lumen dimensions after stent placement. Second, IVUS-guided stent implantation yields larger acute stent dimensions. Third, IVUS-guided therapy in the form of additional stent placement or use of a larger balloon does not increase stent procedure complication rates when appropriate criteria for optimal stent placement are used. A randomized clinical trial (AVID) of angiography-directed versus IVUS-directed coronary stent placement is in progress (with a second soon to begin enrollment). In this trial, ultrasound guidance has been shown to improve acute procedural results, providing larger lumen dimensions without an increase in complication rates. IVUS guidance, however does not appear to affect the incidence of stent thrombosis within 30 days in the present era of high-pressure balloon inflations and aggressive antiplatelet therapy. Results concerning the effect of ultrasound-guided therapy on long-term target lesion revascularization rates are pending. To date, IVUS imaging has greatly contributed to advancements in coronary stent placement techniques. The future of IVUS-guided coronary stent placement will, of course, depend on the results of several ongoing clinical trials.

Computerized assessment of coronary lumen and atherosclerotic plaque dimensions in three-dimensional intravascular ultrasound correlated with histomorphometry

Intravascular ultrasound (IVUS), which depicts both lumen and plaque, offers the potential to improve on the limitations of angiography for the assessment of the natural history of atherosclerosis and progression or regression of the disease. To facilitate measurements and increase the reproducibility of quantitative IVUS analyses, a computerized contour detection system was developed that detects both the luminal and external vessel boundaries in 3-dimensional sets of IVUS images. To validate this system, atherosclerotic human coronary segments (n = 13) with an area obstruction > or = 40% (40% to 61%) were studied in vitro by IVUS. The computerized IVUS measurements (areas and volumes) of the lumen, total vessel, plaque-media complex, and percent obstruction were compared with findings by manual tracing of the IVUS images and of the corresponding histologic cross sections obtained at 2-mm increments (n = 100). Both area and volume measurements by the contour detection system agreed well with the results obtained by manual tracing, showing low mean between-method differences (-3.7% to 0.3%) with SDs not exceeding 6% and high correlation coefficients (r = 0.97 to 0.99). Measurements of the lumen, total vessel, plaque-media complex, and percent obstruction by the contour detection system correlated well with histomorphometry of areas (r = 0.94, 0.88, 0.80, and 0.88) and volumes (r = 0.98, 0.91, 0.83, and 0.91). Systematic differences between the results by the contour detection system and histomorphometry (29%, 13%, -9%, and -22%, respectively) were found, most likely resulting from shrinkage during tissue fixation. The results of this study indicate that this computerized IVUS analysis system is reliable for the assessment of coronary atherosclerosis in vivo.